Modeling and Inversion of Local Magnetic Anomalies

Research areas:
J. Geophys. Eng.
We present a method ~ named as MILMA for modelling
and inversion of local magnetic anomalies ~ that
combines forward and inverse modelling of
aeromagnetic data to characterize both magnetization
properties and location of unconstrained local
sources. Parameters of simple-shape magnetized
bodies (cylinder, prism or sphere) are first
adjusted by trial and error to predict the
signal. Their parameters provide a priori
information for inversion of the measurements. Here,
a generalized nonlinear approach with a
least-squares criterion is adopted to seek the best
parameters of the sphere (dipole). This inversion
step allows the model to be more objectively
adjusted to fit the magnetic signal. The validity of
the MILMA method is demonstrated through synthetic
and real cases using aeromagnetic
measurements. Tests with synthetic data reveal
accurate results in terms of depth source, whatever
be the number of sources. The MILMA method is then
used with real measurements to constrain the
properties of the magnetized units of the
Champtoceaux complex (France). The resulting
parameters correlate with the crustal structure and
properties revealed by other geological and
geophysical surveys in the same area. The MILMA
method can therefore be used to investigate the
properties of poorly constrained lithospheric
magnetized sources.